Compressor arrangement with integrated motor

ABSTRACT

A rotary compressor arrangement includes a stationary member centered at a shaft axis and a rotary member rotating around the stationary member; the stationary member and the rotary member being inside a hermetically sealed inner volume within the rotary compressor arrangement; the rotary compressor arrangement comprising a stator with a winding arrangement generating an electromagnetic force inside the stator, the stator being arranged outside the hermetically sealed inner volume; the rotary compressor arrangement further comprising a plurality of magnets directly attached to the rotary member and facing the winding arrangement in the stator such that the rotary member is entrained in rotation by a rotating electromagnetic field from the stator.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 16/332,188 filed Mar. 11, 2019, which is a National Stage ofInternational Application No. PCT/EP2017/072841, filed on Sep. 12, 2017,which claims priority to European Application No. 16189071.0, filed onSep. 15, 2016, the entire contents of which are being incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention is directed to a compressor arrangement comprisingan integrated motor and, more specifically, to a rotary compressorarrangement of the vane type preferably used in a cooling orrefrigerating system.

BACKGROUND OF THE INVENTION

Currently, different types of compressors are used in cooling orrefrigeration systems. Gas compressors are mechanical devices increasingthe pressure of a gas by reducing its volume: by changing the state ofthe gas, its temperature is also changed. Therefore, when the gas passesthrough a condenser, it can be used as refrigerant in a refrigerationcompressor.

For home applications, vane rotary compressors are commonly used asrefrigeration compressors thanks to their reduced size. Typically, avane rotary compressor comprises a circular rotor rotating inside of alarger circular cavity configured by the inner walls of the compressorhousing. The centers of the rotor and of the cavity are offset, causingeccentricity. Vanes are arranged in the rotor and typically slide intoand out of the rotor and are tensioned to seal on the inner walls of thecavity, in order to create vane chambers where the working fluid,typically a refrigerant gas, is compressed. During the suction part ofthe cycle, the refrigerant gas enters through an inlet port into acompression chamber where the volume is decreased by the eccentricmotion of the rotor and the compressed fluid is then discharged throughan outlet port.

While small sized vane rotary compressors are advantageous, leaking ofrefrigerant through the surfaces of the inner walls of the compressorhousing is disadvantageous. This is why these compressors also uselubricating oil, having two main functions: one is to lubricate themoving parts, and the second one is to seal the clearances between themoving parts, which minimizes gas leakage that can adversely affect theefficiency of the compressor.

There exist different types of refrigeration compressors, varyingdepending on their configuration. Typically, refrigeration compressorscan be open, semi-hermetic or hermetic. In hermetically sealedcompressors, the compressor and its driving motor are coupled to a sameshaft and are enclosed in a rigid hermetic casing. This type ofhermetically sealed compressors are air tight and ensure no leakage ofthe working fluid to the outside. They are typically used in domesticrefrigerators at home, in freezers or in air conditioners, for example.Semi-hermetic compressors also comprise inside a casing the compressorand its driving motor; however, this casing can be opened in order toaccess both the motor and the compressor itself in case of reparationsbeing needed. On the other hand, open compressors are configured with noencasing of the compressor or the motor, so they are not leak proof andare susceptible to leak, relying on shaft seals, which need to belubricated, to prevent leakage of working fluid and to maintain internalpressure.

One of the main advantages of a hermetic compressor is that it isconfigured as a single unit so it can be easily transported, thanks toits compactness. Moreover, it is less noisy and its installation is veryeasy. However, this compressor is typically not intended to be repairedso, when a problem arises, it is the whole unit which is replaced by anew one.

Semi-hermetic compressors are easier to repair compared to hermeticcompressors, as they are accessible. However, certain leakages takeplace causing a certain loss of performance of the compressor.

In both hermetic and semi-hermetic compressors, the electronics andwiring inside the casing are subjected to very high temperatures as theyare arranged inside this hermetical encasing, which makes these types ofcompressors costly. Also, an eventual burnout of the windings cancontaminate the whole system.

On the other hand, in open configurations, the compressor and the motorare easily accessible to be repaired in case of failure, the maintenancebeing cheap and easy. The motor outside of the hermetic chamber allowsmore variety in the motor selection and the use of cheaper motor typesas they work at ambient conditions. The disadvantages of suchconfiguration are that these compressor types are noisy, not compact anda certain gas leakage exists at the motor/chamber connection, whichcauses a loss of its performance. Moreover, lubricating oil is needed inthe shaft seals so that they maintain their sealing properties.

It would therefore be desirable to provide a compressor having theadvantages of the open, hermetic and semi-hermetic compressors, avoidingat the same time their disadvantages.

It is known in the state of the art, for example in document EP 2307734B1, a rotary compressor arrangement having a rotating shaft where themotor structure is integrated inside the compressor arrangement. Thewhole structure is encased by an external housing hermetically sealinginside both the motor and the compressor, therefore constituting ahermetic compressor. This structure is compact but presents thedisadvantage of the high temperatures reached in the electroniccomponents inside, which cannot be properly refrigerated.

The compressor arrangement according to the present invention provides acompact, hermetic, yet silent and cost effective solution: thecompression chamber is in a sealed internal volume; the electronic partsare outside and work at ambient conditions, and there is no directphysical connection between them, so any leakage is prevented.

OBJECT AND SUMMARY OF THE INVENTION

According to a first aspect, the invention relates to a rotarycompressor arrangement 100 comprising a stationary member 40 centered ata shaft axis X and a rotary member 90 rotating around the stationarymember 40; the stationary member 40 and the rotary member 90 are insidea hermetically sealed inner volume 120 within the compressor arrangement100; the compressor arrangement 100 comprises a stator 210 with awinding arrangement 211 generating an electromagnetic force inside thestator 210, the stator 210 being arranged outside the hermeticallysealed inner volume 120. The compressor arrangement of the inventionfurther comprises a plurality of magnets 221 directly attached to therotary member 90 and facing the winding arrangement 211 in the stator210 such that the rotary member 90 is entrained in rotation by arotating electromagnetic field from the stator 210.

According to a preferred embodiment, the rotary compressor arrangement100 of the invention further comprises a rolling member 10 eccentricallyarranged with respect to the stationary member 40 such that a chamber iscreated between them; the arrangement 100 further comprising at leastone satellite element 50 entrained in rotation by the rotary member 90;the at least one satellite element 50 orbiting at an offset axis Y andentraining in rotation the rolling member 10 and ensuring a contactbetween the stationary member 40 and the rolling member 10.

Preferably, the rotary compressor arrangement of the invention furthercomprises an upper plate and a lower plate arranged to close in heightin a tight manner at least one compression chamber 110 created betweenthe stationary member 40 and the rolling member 10.

Typically, the rotary compressor arrangement further comprises at leastone segment element arranged between the upper and/or lower plates toallow a tight sealing of at least one compression chamber 110 and themovement of the rolling member 10. The at least one segment element 80preferably comprises a low friction material.

In the rotary compressor arrangement of the invention, preferably atleast a pair of satellite elements 50, 50′ is arranged in height in therotary member (90) in such a way that the magnets 221 are locatedbetween them.

Typically, in the rotary compressor arrangement of the invention, therotary member 90 is configured as a cylinder, the magnets 221 beingdirectly attached in an external diametric circumference of it.

Typically, the satellite elements are mounted over bearings 300,preferably ball bearings.

In the rotary compressor arrangement of the invention, the stator 210typically comprises a laminated magnetic core embedded in a resinmaterial, the stator 210 being an integral part of the motor housing230.

According to a preferred embodiment, the distance separating the windingarrangement 211 and the magnets 221 in the rotary compressor arrangementof the invention is as small as possible typically smaller than around 1mm.

The rotary compressor arrangement of the invention preferably furthercomprises at least one sealing piston 30 slidable within the stationarymember 40 during rotation of the rolling member 10 creating at least onecompression chamber 110 whose volume is decreased by rotation of therolling member 10 so that a compressible fluid, preferably a refrigerantgas, is compressed before being discharged.

Typically, in the rotary compressor arrangement of the invention,lubricating oil is also provided together with the compressible fluid,compatible with it.

According to a second aspect, the invention refers to acooling/refrigerating system comprising a rotary compressor arrangement100 as the one previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, advantages and objects of the present invention willbecome apparent for a skilled person when reading the following detaileddescription of embodiments of the present invention, when taken inconjunction with the figures of the enclosed drawings.

FIG. 1 shows a representative view of the main components in acompressor arrangement with integrated motor according to the presentinvention.

FIG. 2 shows an external view of the compressor arrangement withintegrated motor according to the present invention, as shown in FIG. 1.

FIG. 3 shows a representative view of the stator of the motor and themagnets of the motor in a compressor arrangement with integrated motoraccording to the present invention.

FIG. 4 shows a representative view of the arrangement of the stator andwindings and the rotary element in a compressor arrangement withintegrated motor according to the present invention.

FIG. 5 shows a sectional view of a compressor arrangement withintegrated motor according to the present invention.

FIG. 6 shows a top view of the compressor arrangement with integratedmotor according to the present invention.

FIGS. 7a-b-c show exploded views of the external configuration, therotary element comprising magnets and the stator comprising windings,respectively, in a compressor arrangement with integrated motoraccording to the present invention.

FIGS. 8a-b-c-d show exploded views of the external configuration, therotary element comprising magnets, the rolling element, vane andstationary body, and the stator comprising windings, respectively, in acompressor arrangement with integrated motor according to the presentinvention.

FIG. 9 shows a representative view of the arrangement of the upper andlower plates, one or more segment elements, and the rolling memberwithin the compressor arrangement with integrated motor according to thepresent invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As shown in FIG. 6 for example, the present invention relates to a vanerotary compressor arrangement, called in what follows rotary compressorarrangement 100 or simply rotary compressor 100. The rotary compressor100 of the invention is preferably used in cooling or refrigeratingsystems, and the working fluid is typically any compressible gas,preferably a refrigerant gas or a mixture comprising a refrigerant gas.

The rotary compressor 100 comprises an inlet 130 through which theworking fluid enters the compressor and an outlet 140 through which thisfluid, once compressed, exits the mentioned compressor.

In a preferred embodiment of the invention, as it can be seen forexample in FIG. 8c , the compressor further comprises a rolling member10 inside of which a stationary body 40 is arranged centered by a shaftaxis X. The compressor also comprises a vane or sealing piston 30 whichcan slide into a slot 31 in order to contact the internal walls of therolling member 10 and create a tight compression chamber where fluidwill be compressed, as it will be further explained in more detail. Asshown in FIG. 8c , the stationary body 40 is arranged eccentricallyinside the rolling member 10. Referring back to FIG. 6, the inlet 130and the outlet 140 for the working fluid are arranged in the stationarybody 40, and are preferably arranged in the vicinity of the sealingpiston 30.

The arrangement of the invention is made in such a way that the shaft(and shaft axis X) and the stationary body 40 are one single piecewithin the rotary compressor 100 and are static. However, it is therolling member 10 which rotates around the body 40, in fact which rollsover the external surface of the stationary body 40 entrained inrotation by means of at least one satellite element 50, as it will beexplained further.

The sealing piston 30 is slidable within the slot 31 arranged in thebody 40: pressure is maintained in this slot 31 to make the sealingpiston 30 contact the inner wall of the rolling member 10 during thewhole rolling of the rolling member 10 around the stationary body 40.For this to happen there exists a tensioning device inside the slot 31exerting pressure over the sealing piston 30 so that it contacts theinner wall of the rolling member 10: any kind of tensioning deviceproviding such functionality can be used, typically a spring, though apneumatic device is also possible. In the arrangement of the presentinvention, as shown in FIG. 6, the sealing piston 30 creates acompression chamber 110 of a variable volume. More than one sealingpiston can be used in different embodiments of the invention, thereforecreating more than one compression chamber.

In the rotary compressor arrangement of the invention, the referentialsystem is actually inverted: the body 40 is stationary and it is therolling member 10 which is made to roll over it by a pressure exerted bythe at least one satellite element 50 when rotating over it.

The arrangement of the invention also comprises at least one satelliteelement 50 mounted on a rotary member 90: by the rotation of this rotarymember 90, the satellite element 50 is pushed over the rolling member 10and rolls around it, pushing it towards the stationary body 40.Therefore, there exists a contact (typically, when the stationary body40 and the rolling member 10 are cylindrically shaped, there exists alongitudinal contact line) between the rolling member 10 and the body40, all the time while the rotary member rotates around the rollingmember 10. It is also evident that this contact is aligned with thelocation of the satellite element 50. By the sealing piston 30contacting the inner walls of the rolling member 10, a tight compressionchamber 110 is created having variable volume (decreasing with time)where the working fluid is compressed before being discharged.

The satellite element is arranged offset from the axis X, at an axis Yas shown for example in FIG. 5, and is made to orbit around thestationary body 40. The satellite element 50 contacts the external wallof the rolling member 10 under certain pressure or force (i.e. thedistance between the axis X and Y is such that this force is exerted andmaintained during the whole orbiting of the satellite element): asexplained before, this contact of the satellite element 50 and theexternal wall of the rolling member 10 under pressure makes that thesatellite element 50 entrains in rotation (actually rolls over) therolling member 10 over the stationary body 40, similar as in a geararrangement.

When looking for example at FIG. 7b or 8 b, a pair of satellite elements50 and 50′ for example are arranged at a certain height, pressing overthe external wall of the rolling member 10, aligned with an innercontact of the stationary body 40 and the rolling member 10. TheseFigures also represent for example another pair of satellite elements50″ and 50′″, arranged in height and also pressing over the externalwall of the rolling member 10: in this configuration, the contact of theinner walls of the rolling member 10 with the stationary body 40 in anintermediate point between the external contacts of the pairs ofsatellite elements 50, 50′ and 50″, 50″.

The satellite elements are typically mounted over bearings 300,preferably ball bearings, as shown for example in FIG. 1 or 4.

Typically, the compressor arrangement of the invention works with arefrigerant gas as working fluid, and oil is also entrained with therefrigerant in the compressor, in order to lubricate the moving partsand to seal the clearances or gaps between them. Oil is preferablyintroduced in the compressor by an oil pump (not shown) and there isalso typically provided a device (not shown) to gather this oil andreturn it to the oil pump so that it is pumped once again together withthe refrigerant. The lubricating oil may be any oil compatible with therefrigerant used as working fluid in the compressor. The refrigerant maybe any suitable refrigerant that is effective in a given temperaturerange of interest.

As shown in FIG. 9, the compressor arrangement of the inventiontypically comprises an upper plate 70 and a lower plate 60 closing theupper and lower parts of the compressor, thus sealing the compressionchamber 110 created together with the sealing piston 30. For example,the upper plate 70 and the lower plate 60 are arranged at the upper part11 and the lower part 12 of the rolling member 10. The distance betweenthe two plates 70, 60 and the height of the body configuring the rollingmember 10 must be precise in order to correctly seal and create thecompression chamber 110, though a certain clearance adjustment orcompensation is feasible acting on the satellite element(s). However, noother parts configuring the compressor arrangement of the invention areneeded to be done with precise tolerances as it is the case in the knownprior art, which makes this arrangement much easier to be manufacturedand consequently less costly.

Typically, at least one segment element 80 is further arranged betweenthe upper and/or lower plates 70, 60 to allow a tight sealing of thecompression chamber 110 and at the same time allow the movement of therolling member 10. This arrangement is done in such a way that lowerfriction in the movement of the rolling member 10 with respect to thestationary body 40 and the plates 60, 70 is allowed. The rotarycompressor 100 illustrated in FIG. 9 includes two segment elements 80,each positioned above and below the rolling member 10 and the stationarymember 40 adjacent to the upper plate 70 and the lower plate 60,respectively. Preferably, the material configuring the segment elementis a low friction material, typically Teflon®.

These low friction materials allow long life solutions typically inapplications where the sliding action of parts is needed, still with lowmaintenance being required. The friction characteristics of a materialare given typically by the coefficient of friction, which gives a valueshowing the force exerted by a surface made of such a material when anobject moves across it, such that a relative motion exists between thetwo, the object and the surface. Typically, for Teflon, this coefficientof friction is comprised between 0.04 and 0.2. Low friction materialshave a coefficient of friction below 0.4, more preferably below 0.3 andeven more preferably below 0.2.

The object of the invention is to integrate the driving motor structureinto the arrangement of a rotary vane compressor itself. This motorintegration according to the invention can be done in compressorarrangements having a fixed shaft axis (or stationary body 40 togetherwith a shaft axis X) and an external rotating part (in this case, anexternal rotary member 90). In a preferred embodiment of the invention,the configuration of the compressor arrangement 100 comprises satelliteelements mounted in the rotary member 90, pushing the rolling member 10over the stationary body 40, as discussed. The windings 211 are mountedon an external stator 210, while magnets 221 are directly attached ontothe external surface of the rotary member 90, directly facing thesewindings 211, with no metallic element arranged in between. The distancebetween the magnets and the windings shall be free and as small aspossible, typically below around 1 mm; otherwise the efficiency willdrop drastically and would be impossible to rotate the rotor.

When electrical current circulates through the windings 211 anelectromagnetic force or field is generated inside the stator 210: thesewindings work as electromagnets and therefore have poles, the oppositepoles of which are in the magnets 221 directly attached to the rotarymember 90. The magnetic fields created between these poles are designedto orientate and create forces providing a torque in the rotary member90 making it rotate.

It is evident that in classical rotary compressors such an arrangementfor the windings and the magnets would not be possible because there isno external rotating element where the magnets could be attached andwhere they could face directly (without any metallic elementsinterposed) the windings in the rotor. The configuration of the presentinvention is particularly advantageous as it integrates the rotor of thecompressor (rotating part of the compressor arrangement, the rotarymember 90) with the rotor of the motor (i.e. where the permanent magnetsare) in one single element, therefore providing a compact and hermeticsolution. Moreover, the windings of the stator are arranged externallyand can be advantageously refrigerated compared to hermetic solutionswhere they are inside a closed chamber. The chamber hermetically sealedin the arrangement 100 of the invention groups inside the body 40, therolling member 10, the rotary element 90 and the magnets 221, as shownfor example in FIG. 5. The stator 210 together with the windings 211 canbe therefore arranged outside this hermetic chamber 120 and can beeasily refrigerated, as shown in any of FIG. 1 or 2, for example.

The stator 210 in the arrangement of the invention typically comprises alaminated magnetic core embedded in a resin, being configured as anintegral part of the motor housing (the stator 210 constitutes thevertical part of the motor housing). The laminated magnetic coretypically comprises a plurality of thin metallic sheets lyingessentially parallel with the lines of flux, so the magnetic core ismade equivalent to many individual magnetic circuits, each one receivinga small fraction of the magnetic flux, therefore highly restricting mostof the flow of Eddy currents.

In general terms, the arrangement of the invention proposed the use ofthe rotary part of the compressor to be used as well as the rotor of themotor. This allows a direct driving of this rotary part, which highlyreduces the number of parts and the noise. The final structure of thecompressor arrangement is very solid and compact and is made able towithstand 20 bars of pressure remaining tight for the refrigerant gasused. Also by the use of the bearings over which the rotary part ismounted, the arrangement is made very compact. Also, heat dissipationfrom the stator is improved as it is directly in contact with externalair. The rigid structure of the magnetic circuit integrated in thecompressor arrangement therefore contributes to the mechanicalresistance of the motor housing.

Referring now to the Figures attached, FIG. 1 shows the arrangement ofthe stationary body 40 eccentrically surrounded by the rolling member10, which is made to roll over the external walls of the body 40 bymeans of the rotary member 90 mounted over bearings 300. Magnets 221 aredirectly attached onto the outer wall of the rotary member 90, facingcorresponding windings 211 in the stator 210. The typical laminatedstructure of the stator is not represented in this Figure, though.

FIG. 2 shows the whole compressor arrangement 100 seen from the outside,as a full compact structure with the motor housing 230 outside, showingthe stator 210 sheltering inside the windings 211. FIG. 3 shows wherethese windings are located inside the stator 210 and how they face(floating view) the magnets 221.

FIG. 4 shows where the satellite elements would be arranged within thecompressor, mounted on the rotary member 90.

FIG. 5 shows a sectional view of the compressor arrangement according toa preferred embodiment of the invention, showing the hermetic chambergrouping inside the magnets 221, the rotary member 90, the rollingmember 10 and the stationary body 40. The stator 210 with the windings211 is arranged outside this hermetic chamber.

FIG. 6 shows the structure of a rotary vane compressor with a fluidinlet 130 and a fluid outlet 140 for the fluid once it has beencompressed. It is shown the sealing piston 30 which can slide into aslot 31 in order to contact the internal walls of the rolling member 10and create a tight compression chamber 110 where fluid is compressedbefore being discharged through the outlet 140. Two satellite elementsare shown, 50 and 50″ which push the rolling member 10 over thestationary body 40 to vary the volume of the chamber 110. It can be seenhere how the contact of the inner walls of the rolling member 10 withthe outer walls of the stationary body 40 occurs at an intermediateangular location between the external contacts of the satellite elements50 and 50″ with the rolling member 10.

FIGS. 7a, 7b and 7c show the motor housing 230 with the stator 210 (FIG.7a ); the rotary member 90 with the magnets 221 attached outside and howa pair of satellite elements 50, 50′ and another pair of satelliteelements 50″, 50′″ are arranged in height in this member 90 to push androll over the rolling member 10 (FIG. 7b ); the stator configuration 210with the windings 211, which will be face the magnets 221 (FIG. 7c ).

FIGS. 8a, 8b, 8c and 8d show the motor housing 230 with the stator 210(FIG. 8a ); the rotary member 90 with the magnets 221 attached outsideand how a pair of satellite elements 50, 50′ and another pair ofsatellite elements 50″, 50′″ are arranged in height in this member 90 topush and roll over the rolling member 10 and between which the magnets221 are arranged (FIG. 8b ); the rolling member 10 eccentricallyarranged over the stationary body 30 and the sealing piston 30contacting the inner wall of it (FIG. 8c ); the stator configuration 210with the windings 211, which will be face the magnets 221 (FIG. 8d ).

Although the present invention has been described with reference topreferred embodiments thereof, many modifications and alternations maybe made by a person having ordinary skill in the art without departingfrom the scope of this invention which is defined by the appendedclaims.

1. A rotary compressor arrangement comprising: a stationary membercentered at a shaft axis and a rotary member rotating around thestationary member; the stationary member and the rotary member beinginside a hermetically sealed inner volume within the rotary compressorarrangement; a stator with a winding arrangement generating anelectromagnetic force inside the stator, the stator being arrangedoutside of the hermetically sealed inner volume; a plurality of magnetsdirectly attached to the rotary member and facing the windingarrangement in the stator such that the rotary member is entrained inrotation by a rotating electromagnetic field from the stator; a rollingmember eccentrically arranged with respect to the stationary member suchthat at least one compression chamber is created between them; an upperplate and a lower plate arranged at an upper part and a lower part,respectively, of the rolling member, sealing the at least onecompression chamber created between the stationary member and therolling member; and at least one segment element arranged between theupper and lower plates to allow a tight sealing of the at least onecompression chamber and the movement of the rolling member, the at leastone segment element comprising a low friction material.
 2. The rotarycompressor arrangement according to claim 1 further comprising: at leastone satellite element entrained in rotation by the rotary member, the atleast one satellite element orbiting at an offset axis and entraining inrotation the rolling member and ensuring a contact between thestationary member and the rolling member.
 3. The rotary compressorarrangement according to claim 2 wherein at least a pair of satelliteelements is arranged in height in the rotary member in such a way thatthe plurality of magnets are located between them.
 4. The rotarycompressor arrangement according to claim 1 wherein the rotary member isconfigured as a cylinder, the plurality of magnets being directlyattached in an external diametric circumference of the rotary member. 5.The rotary compressor arrangement according to claim 2 wherein thesatellite elements are mounted over bearings.
 6. The rotary compressorarrangement according to claim 5 wherein the bearings are ball bearings.7. The rotary compressor arrangement according to claim 1 wherein thestator comprises a laminated magnetic core embedded in a resin material,the stator being an integral part of a motor housing.
 8. The rotarycompressor arrangement according to claim 1 wherein a distanceseparating the winding arrangement and the plurality of magnets is lessthan around 1 mm.
 9. The rotary compressor arrangement according toclaim 1 further comprising at least one sealing piston slidable withinthe stationary member during rotation of the rolling member creating theat least one compression chamber whose volume is decreased by rotationof the rolling member so that a compressible fluid is compressed beforebeing discharged.
 10. The rotary compressor arrangement according toclaim 9 wherein the compressible fluid comprises a refrigerant gas. 11.The rotary compressor arrangement according to claim 9 wherein alubricating oil is provided with the compressible fluid.
 12. The rotarycompressor arrangement according to claim 1 wherein the low frictionmaterial has a coefficient of friction below 0.4.
 13. Acooling/refrigerating system comprising a rotary compressor arrangementcomprising: a stationary member centered at a shaft axis and a rotarymember rotating around the stationary member; the stationary member andthe rotary member being inside a hermetically sealed inner volume withinthe rotary compressor arrangement; a stator with a winding arrangementgenerating an electromagnetic force inside the stator, the stator beingarranged outside of the hermetically sealed inner volume; a plurality ofmagnets directly attached to the rotary member and facing the windingarrangement in the stator such that the rotary member is entrained inrotation by a rotating electromagnetic field from the stator; a rollingmember eccentrically arranged with respect to the stationary member suchthat at least one compression chamber is created between them; an upperplate and a lower plate arranged at an upper part and a lower part,respectively, of the rolling member, sealing the at least onecompression chamber created between the stationary member and therolling member; and at least one segment element arranged between theupper and lower plates to allow a tight sealing of the at least onecompression chamber and the movement of the rolling member, the at leastone segment element comprising a low friction material.